1. Field of the Invention
The present invention relates to an insert terminal containing case and a piezoelectric electroacoustic transducer including the case.
2. Description of the Related Art
Piezoelectric electroacoustic transducers, such as a piezoelectric sounder and a piezoelectric receiver that produce alarm sounds and operation sounds, have been widely used in electronic devices, household electric appliances, mobile phones, or the like. An exemplary piezoelectric electroacoustic transducer includes a piezoelectric diaphragm placed in an insert terminal containing case and bonded with the insert terminal containing case without an air leakage, and a cover having a sound-emitting hole, the cover being bonded to an opening at the upper portion of the case. One example of this piezoelectric diaphragm is a unimorph piezoelectric diaphragm in which a piezoelectric component made of a piezoceramic is bonded to a surface of a metal plate. Another example of this piezoelectric diaphragm is a bimorph piezoelectric diaphragm including a laminated piezoceramic.
FIG. 15 shows an example of a piezoelectric electroacoustic transducer described in Japanese Unexamined Patent Application Publication No. 2003-58166. The transducer includes a case 40, a piezoelectric diaphragm 42 contained in the case 40, and terminals 43 provided on the case 40 by insert molding. A supporting portion 45 is provided at the inner periphery of the case 40. The piezoelectric diaphragm 42 is supported by the supporting portion 45. An elastic insulator 48 covers edges of the piezoelectric diaphragm 42. A conductive adhesive 46 is applied on the insulator 48 to electrically connect the piezoelectric diaphragm 42 with the terminal 43. After application of the conductive adhesive 46, the periphery of the piezoelectric diaphragm 42 is fixed to the case 40 with an elastic adhesive such as silicone rubber (not shown), and a cover (not shown) is bonded to the opening at the upper portion of the case 40.
To ensure electrical continuity to the conductive adhesive 46, the terminal 43 needs to be exposed at the inside of the case 40 by a predetermined length. However, when the terminal 43 is exposed in the horizontal direction as shown in FIG. 15, the dimension S of the piezoelectric diaphragm 42 must be reduced by the exposed length of the terminal 43 compared with the opening dimension L. In recent years, trends towards miniaturization of electronic devices have also required miniaturization of piezoelectric electroacoustic transducers. Miniaturization of the case 40 means a reduction in the dimension S of the piezoelectric diaphragm 42. The reduction in the dimension S of the piezoelectric diaphragm 42 increases its resonance frequency, which causes a reduction in sound pressure, and is thus undesirable. Therefore, to reduce the resonance frequency and increase the sound pressure, it is important to achieve the minimum difference between the opening dimension L of the case 40 and the dimension S of the piezoelectric diaphragm 42.